National Semiconductor's New Clock Jitter Cleaners Eliminate Need For VCXO Modules

PowerWise LMK04000 Family's Industry-leading Sub-200 Femtosecond Jitter Enhances System Performance and Accuracy

Santa Clara, CA - National Semiconductor Corp. recently introduced the industry's first family of clock jitter cleaners capable of providing ultra low-noise clocks without external high-performance voltage-controlled crystal oscillator (VCXO) modules. Using a simple external crystal and cascaded PLLatinum architecture, National's new clock jitter cleaners provide sub-200 femtosecond (fs) root- mean-square (RMS) jitter to improve system performance and accuracy. This level of performance rivals the most expensive VCXO modules.

The new LMK04000 family consists of five precision clock conditioners: LMK04000B, LMK04001B, LMK04011B, LMK04031B and LMK04033B. These devices feature power-to-noise specifications that place them among National's PowerWise family of energy-efficient products. The LMK04000B and LMK04001B offer 24.4 mW-ps per channel, while the LMK04031B and LMK04033B are rated at 25.4 mW-ps per channel and the LMK004011B is 37.4 mW-ps per channel.

The LMK04000 devices provide clean clocks to analog-to-digital converters (ADC), digital-to-analog converters (DAC) and other high-performance components used in wireless infrastructure, test and measurement, and medical ultrasound and imaging equipment. Wireless base station applications include single-carrier and multi-carrier GSM (GSM), Long Term Evolution (LTE), Universal Mobile Telecommunications System (UMTS), Worldwide interoperability for Microwave Access (WiMAX) and Code Division Multiple Access (CDMA) networks.

These clock conditioners are well-matched to work with National's high- speed op amps and ADCs -- such as the LMH6552 fully differential amplifier, LMH6514/15 digital variable gain amplifiers and ADC14V155 high-bandwidth 14- bit ADC -- to provide a complete signal-path system solution.

Key Technical Features - Precision Clock Conditioners

The new LMK04000 family uses National's cascaded PLLatinum architecture, which consists of two high-performance cascaded phase-locked loops (PLL), a low-noise crystal oscillator circuit, a high-performance integrated VCO as well as low-noise dividers and drivers. The first PLL can be configured to use a simple external crystal or a VCXO module to provide the jitter cleaning function while the second PLL uses the integrated VCO to perform low-noise clock generation.

These devices feature dual redundant inputs, five differential outputs and an optional default-clock upon power-up. The input block is equipped with loss of signal detection and automatic or manual selection of the reference clock. Each clock output pair consists of a programmable divider, a phase synchronization circuit, a programmable delay and either a low-voltage differential signaling (LVDS), low-voltage positive-emitter-coupled logic (LVPECL) or low-voltage CMOS (LVCMOS) output driver. The LVPECL and LVDS outputs support clock rates up to 1080 MHz, while the LVCMOS outputs reach up to 250 MHz. The default-clock is available on CLKout2 and it can be used to provide an initial clock for the field-programmable gate array (FPGA) or the microcontroller that programs the clock jitter cleaner during the system power-up sequence.

National's LMK04000 precision clock conditioners are supplied in 48-pin LLP packages. National fabricates these products on its proprietary BiCMOS8 process technology in its South Portland, Maine, facility. This state-of-the- art silicon germanium process enables the devices to achieve the lowest jitter and power performance in the industry.

About National's Communications Infrastructure Solutions
National Semiconductor's communications infrastructure solutions optimize system efficiency, increase power density and deliver robust system performance. Its PowerWise subsystem reference designs solve energy- efficiency problems at an architectural level in a small footprint, thereby reducing cooling requirements while delivering superior performance. National's reference designs and solutions address the specific needs of wired data centers, wireless base stations and merchant power supply applications.

SOURCE: National Semiconductor Corp.